This invention relates to vehicle restraints for use at loading docks.
Prior art vehicle restraints are disclosed in U.S. Pat. Nos. 4,264,259 and 4,648,781, the disclosures of which are incorporated by reference. The vehicle restraints in these patents are attached to a loading dock and include a hook that engages the ICC bar of a trailer to prevent the trailer from moving away from the loading dock. The hook can be rotated by a motor to a down or disengaged position to allow the truck to back up to the dock. The motor is also used to pivot the hook from the down position to an up or engaged position in which the hook engages the ICC bar of the trailer.
In operation, the above-described restraints are stored with the hook in the disengaged position. Once a vehicle is properly positioned at the loading dock with the ICC bar positioned above the hook, the motor is activated to pivot the hook to the engaged position. The motor is controlled by a timer such that the motor shuts off when the motor has rotated the hook for a predetermined length of time. The predetermined length of time corresponds to the time necessary for the motor to cause the hook to rotate from the disengaged position to a full-up position. Somewhere between the disengaged position and the full-up position, the hook engages the ICC bar, at which time a clutch mechanism between the motor and the hook allows the motor to continue to run until the timer shuts the motor off.
The motor used in the prior art vehicle restraint is commonly referred to in the art as a worm gear motor. The worm gear motor has a gear ratio large enough to make the device self-locking. That is, when the power to the motor is turned off, the gears substantially fix the motor output shaft against rotation in either the forward or reverse direction. In this respect, the worm gear motor is self-locking.
One problem with this prior art vehicle restraint is that it relies on the clutch mechanism to hold the hook in place against the ICC bar. A second problem with this prior art device is that it requires the tip of the hook to wrap around the top of the ICC bar to securely restrain the trailer. When a trailer is loaded or unloaded, the rear portion of the trailer typically moves up and down and fore and aft as forklifts travel into and out of the trailer. This motion of the trailer can cause the clutch mechanism to slip, causing the hook to rotate down by small increments. Such movement of the hook is commonly referred to in the art as xe2x80x9chook sag.xe2x80x9d Once the hook has sagged to a certain position (i.e., where the tip of the hook no longer wraps around the top of the ICC bar), it no longer adequately restrains the trailer. This defeats the purpose of the vehicle restraint and creates a potentially dangerous situation in which the trailer is not restrained from movement away from the loading dock.
Such prior art releasable locking devices require constant monitoring of the state of the hook to make sure the bottom of the hook tip does not drop below the top of the ICC bar. In some circumstances, the motor has to be re-activated repeatedly to reposition the hook against the ICC bar. If the hook moves to an unsafe position while the forklift operator is in the trailer, an unsafe condition can exist without the operator being aware.
U.S. Pat. No. 4,648,781 discloses an improvement to the above described device. The improvement comprises automatically re-energizing the motor when the hook sags below a certain position, to thereby raise the hook back into contact with the ICC bar. This improvement may enhance the safety of the device, but its drawback is that it is a very expensive option and is not easily adapted to the old units that are already installed. Furthermore, the prior art improvement can reduce the life of the motor due to the repeated re-energizing of the motor.
The present invention alleviates the above-noted problems by providing a vehicle restraint comprising a base member (e.g., a track), a carriage movably mounted to the base member, and a restraining member (e.g., a pivotable hook) mounted to the carriage and movable between an engaged position and a disengaged position. The restraining member is biased toward the engaged position. By virtue of this arrangement, if the restraining member is forced down due to motion of the vehicle, the restraining member will move back to full engagement with the ICC bar, thereby ensuring full restraining capabilities. This is accomplished without the need to re-energize the motor, and thus is more reliable and will not unduly stress the motor. The present invention is also relatively inexpensive to incorporate into the prior art design, and can be easily field-installed onto existing prior art units.
Preferably, the restraining member is biased by a biasing member in the form of a gas spring that can be operatively positioned between the restraining member and the carriage. In one embodiment, the restraining member is pivotable, and the restraint further includes a lever interconnected with the restraining member. In this embodiment, the biasing member is interconnected with the lever to bias the restraining member toward an engaged position. The biasing member can be positioned to bias the restraining member toward the disengaged position when the restraining member is in the disengaged position and to bias the restraining member toward the engaged position when the restraining member is in the engaged position. In this manner, the restraining member is held in the disengaged position by the biasing member.
The above-described vehicle restraint can be produced by modifying existing vehicle restraints that have a base member, a carriage movably mounted to the base member, and a restraining member mounted to the carriage and movable between an engaged position and a disengaged position. The method comprises the step of interconnecting a biasing member with the restraining member to bias the restraining member toward the engaged position. For example, the interconnecting step can include the step of operatively positioning the biasing member between the carriage and the restraining member.
In one embodiment, the restraining member includes a hook mounted to a shaft. In this embodiment, the interconnecting step comprises the steps of mounting a lever to the shaft and attaching the biasing member to the lever. If the vehicle restraint includes a driven sprocket secured to the shaft, then the method can further include the steps of removing the driven sprocket from the shaft, and mounting a lost-motion sprocket to the shaft. The lost-motion sprocket allows the restraining member to move independent of the motor and clutch.